The present invention relates generally to indexable cutting inserts and associated cutting tools. More specifically, the invention is directed to indexable polygonal cutting inserts, for milling, reaming, boring and the like having a wiper geometry which improves surface finish generated during machining.
It is known in the industry, that each pass of a cutting insert over a workpiece creates a new surface that, under conventional cutting conditions, has a curved geometry substantially corresponding to the curve of the cutting edge around the active cutting corner of the insert. As has been discussed in the literature, the curved surfaces generated result in a part finish, with high and low points that appears xe2x80x9cscallopedxe2x80x9d in cross-section. Surface finish irregularities are recognized in the industry to result from ordinary machining variables such as workpiece deflection, the feed rate, the size of the nose radius of the cutting insert used and the stability of the machining environment. Multiple insert tools create further surface finish irregularities due to manufacturing tolerances that result in variables in insert position.
Wiper inserts have been developed in an attempt to reduce surface finish irregularities and produce a smoother part finish. Wiper inserts refer to cutting inserts having various geometries at or near the active cutting edge or edges such that as the cutting insert travels over the workpiece and cuts an area therefrom, the new surface that is generated by the cutting edge is xe2x80x9cwipedxe2x80x9d or xe2x80x9crubbedxe2x80x9d by a wiper geometry. The wiper geometry is positioned on the insert finish cutting edge.
In the past, conventional wiper inserts have been manufactured by forming curved peripheral flanks having a large radius or a series of radii on the finish cutting edge to remove surface irregularities, for example the feed line. FIG. 1 shows a top view of an example of a conventional insert 100 having a top surface 110 and curved flanks 120. The flanks 120 of the insert extend outward in the plane of the top surface, which gives this conventional insert the appearance, in top view, of a polygon with sides bulging outward. A drawback of conventional designs and cutting methods based on this concept is that the curved nature of the flanks causes seating problems. When multiple flanks and edges of a conventional insert carry such wiper geometries, expensive tooling of toolholder pockets to match the periphery of the insert is required or the insert does not seat properly in the cutting tool holder. Due to such seating problems, the radiused flank geometry is not put on all sides of the insert, thus retaining flanks with the flat surfaces for seating in the pocket. However, this solution reduces the number of usable wiper cutting edges per insert.
Another design used for wiping is a negative crown applied to top and/or bottom insert surfaces, see FIGS. 2a and 2b. The top surface 210 of the insert 200 has a land 220 that descends from the center 290 of the top surface outward and downward to the flanks 230 of the insert. This land intersecting the flanks creates a cutting edge 240 that is lower, with reference to top surface 210, at the corners 250 of the insert than at mid-flank position 260, thereby forming a resulting radius along the insert cutting edges, in this design, the highest point on the finish cutting edge, with reference to the top surface performs the wiping action. Bottom surface 270 also has a land 280, thereby providing additional cutting edges. The negative crown design results in several drawbacks: This prior art design has the highest point on the finish cutting edge fixed at roughly the mid-flank position between the corners adjacent the cutting edge. Thus, the distance from the active cutting corner to the wiper is dictated by the size of the insert A second drawback is increased horsepower required for cutting due to the obtuse angle between flank 230 and land 220. A third drawback is increased cutting force generated in the workplace and the tool due to the negative crown geometry, which results in workplace deflection, chatter and accelerated tool wear. Furthermore, when the negative crown geometry is used on a positive insert, little, if any, positive cutting angle to the workpiece can be achieved and fewer cutting edges are available, and when used on a negative insert no positive cutting or neutral cutting angle to the workpiece can be obtained and the insert has a limited range of angular presentation of the cutting edge to the workplace.
Hence there is seen to be a need in the cutting tool art for providing an indexable wiper insert for mounting in a cutting tool, such as a rotary milling, reaming, boring tool or the like, having positive cutting action that uses all available cutting edges and seats properly in the tool body. There is a further need for an indexable insert wherein the position of the wiping portion of the cutting edge can be varied for machining around fixtures and the like.
An object of the invention is to provide a cutting insert, cutting tool and method of machining that overcomes the limitations of the prior art. It is a further object of the invention to provide an indexable wiper insert having positive cutting action that uses all available cutting edges and seats properly in the tool body. It is a yet further object of the invention to provide a positive geometry wiper wherein the position of the wiping portion of the cutting edge can be varied for machining around fixtures and the like.
One object of the invention is to provide a cutting insert of hard, wear resistant material including a body having substantially polygonal major surfaces, flanks extending therebetween, respective pairs of the flanks intersecting to form corners, at least one pair of cutting edges including a lead cutting edge and a finish cutting edge sharing a common corner and being formed by intersection of a major surface with one of the respective pairs of flanks, wherein the finish cutting edge is a curve in a plane of the flank that forms the finish cutting edge, the curve having an apex proximate the common corner, the curve forming a wiper on the finish cutting edge at or closely proximate to the apex. In another aspect of the invention, the wiper may be positioned a selected distance xe2x80x9cd2xe2x80x9d from the common corner, which can range from 0.5% to 45% of the length of the flank that forms the finish cutting edge. Alternatively, the distance xe2x80x9cd2xe2x80x9d is selected to range from approximately two times the common corner radius to less than half a length of the flank that forms the finish cutting edge
In another aspect of the invention each finish cutting edge extends along a wiper form in the major surface adjacent the finish cutting edge, the wiper form has a positive or neutral geometry.
In another aspect of the invention, the curve includes a first portion defined by a first radius and a second portion defined by a second radius. It is an object of the invention to provide the curve with a second radius that decreases along the finish cutting edge from the wiper to the common corner. Alternatively, the curve may include a first portion defined by a first radius and a second portion defined by a plurality of radii.
It is another object of the invention to provide a cutting insert of hard, wear resistant material including a body having substantially polygonal major surfaces, flanks extending therebetween substantially perpendicular to the surfaces, respective pairs of the flanks intersecting to form corners, at least one pair of cutting edges including a lead cutting edge and a finish cutting edge sharing a common corner and being formed by intersection of a major surface with one of the respective pairs of flanks, the finish cutting edge being curved in a plane of the flank forming the finish cutting edge and having a wiper at a selected position on the finish cutting edge, wherein each finish cutting edge extends along a positive or neutral geometry wiper form in the major surface. Optionally, a chipbreaker form extends along at least a portion of the lead cutting edge.
It is another object of the invention to provide a cutting insert of hard, wear resistant material including a body having substantially polygonal major surfaces, flanks extending therebetween, respective pairs of the flanks intersecting to form corners, cutting edges being formed by intersection of a major surface with the flanks, each cutting edge being a curve in the plane of the respective flank and ascending toward the major surface that forms the cutting edge, the curve having an apex forming a wiper on the cutting edge wherein the wiper is proximate a corner.
In another aspect of the invention, the insert flanks are substantially planar. In yet another aspect of the invention the flanks are substantially perpendicular to the major surfaces such that all cutting edges may be provided with the wiper.
In another aspect of the invention a material removal tool is provided having at least one insert mounted thereto including a body having substantially polygonal major surfaces, flanks extending therebetween, respective pairs of the flanks intersecting to form corners, at least one pair of cutting edges sharing a common corner and being formed by intersection of a major surface with one of the respective pairs of flanks, the insert being positioned in the tool with the common corner as the active cutting corner and the pair of cutting edges including a lead cutting edge and a finish cutting edge wherein the finish cutting edge is a curve in a plane of the flank that forms the finish cutting edge, the curve having an apex proximate the common corner, the apex forming a wiper on the finish cutting edge. An object of the invention is to provide a rotary material removal tool.
It is another object of the invention to provide a method for producing an improved finish on a workpiece, including the steps of selecting an insert comprising a body having substantially polygonal major surfaces, flanks extending therebetween, respective pairs of the flanks intersecting to form corners, cutting edges being formed by intersection of at least one of the major surfaces with the flanks, at least one cutting edge being a curve in the plane of the flank that forms the at least one cutting edge, the curve ascending toward the major surface that forms the at least one cutting edge, the curve having an apex forming a wiper on the at least one cutting edge wherein the wiper is proximate a corner; positioning the cutting insert in a tool holder pocket wherein the corner is active in the use environment during cutting and the cutting edge is presented to the workpiece as a finish cutting edge; securing the cutting insert into the pocket; and machining the workpiece.